1. Field of the Invention
This invention relates to catalytic gas reformers useful to convert a reformable medium to a usable fuel, and more particularly provides reformers of novel non-tubular geometries useful to convert mediums such as hydrocarbons to fuels such as hydrogen and carbon monoxide for use in fuel cell based systems.
2. Description of the Prior Art
Reformers are used throughout process industries to produce a fuel, such as a hydrogen rich stream, by catalytically reacting steam and a hydrocarbon at high temperatures, typically above 1,000.degree. F. The reforming reactions are highly endothermic. The hydrogen is usually consumed on sight by any of several processes, for example, ammonia synthesis, de-aromatization, and hydrodesulfurization. In many cases, methane is used as the hydrocarbon. Large, industrial steam/methane reformer systems operate at 10 to 20 atmospheres of pressure and high gas temperatures in the range of 1500.degree. to 2000.degree. F. These operating conditions have been carried out through a tubular design, primarily for stress and strength considerations. Catalytic bed volume in these units typically has considerable excess capacity, on the order of 50%. Hence, reformer tube dimensions of up to 6 inches in diameter by 30 to 50 feet long are common in refinery operations.
Furthermore, unit thermal efficiency of the large industrial reformers is low, but the actual overall system efficiency is substantially higher as the waste heat and undesired products are often utilized by other site processes.
A stand-alone reformer, producing hydrogen for a fuel cell based generation system, should preferably achieve higher unit efficiencies. Therefore, increasing heat transfer and hydrogen production while decreasing waste heat, size, and undesirable byproducts becomes of high importance.
A high efficiency tubular design has been presented, and is described in a paper presented by O. L. Oleson et al, October, 1979, entitled "The UTC Steam Reformer". Similar reformer designs are described in U.S. Pat. Nos. 4,071,330, 4,098,587, 4,098,588, 4,098,589, and 4,203,950, issued to United Technologies Corporation. The designs all include regenerative heat exchange for thermal efficiency, and a tubular arrangement. While designs of this type will perform admirably, improvements can be made. Units which are lower in cost and easier to fabricate and assemble are desirable. Additionally, reformers having configurations more compatible with the addition of fins, pins, or other heat transfer augmentation means are more attractive. And, reformers offering higher heat transfer area per unit bed volume will increase efficiency.
It is thus desirable to provide reformers which offer advantages in these areas. It is particularly beneficial to provide efficient catalytic reformers useful in the preparation of fuels such as hydrogen and carbon monoxide for utilization in fuel cell based power generation systems.